The present invention relates to a dot-matrix liquid crystal display system having a liquid crystal cell containing a multiplicity of matrix elements selectively drivable for displaying a variety of patterns such as characters, graphical images or the like.
There have heretofore been proposed dot-matrix liquid crystal displays including thin-film transistors assembled as drivers into a small-size liquid crystal cell for selectively driving matrix elements. To energize such transistors, a multiplicity of terminals are drawn out of the liquid crystal cell. It is quite tedious and timeconsuming to connect such terminals to a driver circuit. More specifically, a dot-matrix color liquid crystal display has matrix elements each composed of three dots of red, blue and green which are to be selectively driven. The number of terminals connected to such a color liquid crystal display is much greater than that of a single-color or black-and-white liquid color display. In case the number of matrix elements is 100.times.100=10,000, for example, the number of terminals extending from a single-color liquid crystal cell is 100+100=200, while the number of terminals from a color liquid crystal cell is 100+3.times.100=400 as the number of dots required is 100.times.100.times.3=30,000. The procedure for connecting such terminals to the driver circuit is quite complex.
Thin-film transistors are assembled in conventional liquid crystal cells as follows: Gate and matrix element electrodes are directly formed on an inner surface of a substrate of the liquid crystal cell, and a gate insulation film is deposited all over the inner surface of the substrate including these electrodes. A semiconductor layer is formed on the gate insulation film in confronting relation to the gate electrodes. Drain and source electrodes are deposited on the semiconductor layer in partially overlapping relation to opposite sides of the gate electrodes with the semiconductor layer and the gate insulation film interposed therebetween. For electric connection of the drain electrodes to the matrix element electrodes, it has been necessary to form holes through the gate insulation film for providing contact between the electrodes. It has also been necessary to deposit a protective film on the thin-film transistors in order to prevent the latter from being exposed to the atmosphere which would degrade the surface semiconductor layer before the thin-film transistors are sealed in the liquid crystal cell. Accordingly, the process of fabricating thin-film transistors in prior liquid crystal cells has necessitated an increased number of steps due to the step of defining contact holes and the step of depositing a protective film. With liquid crystal cells of a large display area, many thin-film transistors have to be fabricated in the liquid crystal cell. The larger the number of fabrication steps, the greater the difficulty in fabricating thin-film transistors of uniform characteristics, and it is more difficult to render all of the produced thin-film transistors free from defects.